Osmosis In Potato Chips

GCSE Biology: Osmosis in a Potato

Aim

To investigate the effect of placing a piece of potato in a given strength of sugar solution.

Prediction

I predict that, as the solution becomes more concentrated the more the cell will shrink, as the water, of higher concentration inside the potato cells, flows down a concentration gradient into the solution, which has a lower concentration of water molecules. If we say that the percentage change when the potato is placed in the 1M solution is x%. I predict that when the solution is 0.5M the percentage change will be 0.5x%, and when the solution is 0.25M strength I hypothesise the change will be 0.25x%.

Variables Description: Dependant Variables

The dependent

variable is plotted on the y-axis. In this experiment this is the change of mass of the potato when it is placed in different strengths of sugar solution.

Variables Description: Independent

Variables

The independent

variable is plotted on the x axis and is what you choose to change in the experiment. In this experiement it is the strength of the sugar solution.

Variables Description: Constant Variables

These stay the same all the way through the experiment and are the fair test rules. In this experiment that are that the amount of sugar solution used must always me 10.0ml. This is to be placed into the test tube. The solution needs to always be at the same temperature. We will make sure that all experiments are at 20 degrees centigrade before we start the experiment. The size of the potato sample that we place into the solution also needs to be kept constant. A mass of 2.5-2.6g is sensible. The diameter is fixed as the potato cork borer always measures to the exact same measurement. We also needs to make sure that the potato is left in the solution for the same time, 30:00 minutes.

Equipment

* Potato

* Standard Sugar Solution

* Wash Bottle

* Test Tubes and Test Tube Rack

* Cork Borer

* Scalpel

* Cutting Board

* Scales accurate to 2.d.p

* 10ml Syringe

* Paper towels

* Ruler

* Stop Watch

Method

1. Firstly, the cork borer needs to be used to cut out a piece of potato at least 4 cm in length. This allows room for trimming off untidy edges.

2.

3. On the cutting board the cylindrical piece of potato needs to be cut to 35mm. Using a ruler, measure this as accurately as possible and cut the potato to 35mm in length using a scalpel.

4. Using the scaled weigh the potato to 2.d.p. and record the weight.

5. The test tube rack and test tubes need to be assembles. Fill a syringe with exactly 10ml or sugar solution (strength 1M) and empty into a test tube.

6. Now the timing device needs to be reset and readied. An extra pair of hands to aid in the timing may be usful. Ths potato piece can now be placed into the test tube containing 10mb of 1M sugar solution.

7. As the potato piece is placed in the test tube, the timer should be started. After 30 minutes the potato piece needs to be removed from the test tube.

8. Place the potato piece once again on the scales and work out the percentage change.

9. Repeat this experiment for 0.5, 0.25 and 0.125 concentration solutions of sugar solution.

Results

Mass of Chip at... Strength of Solution

1 0.5 0.25 0.125 0.0625 0

Start 2.5 2.6 2.5 2.5 2.5 2.6

End 2.8 2.9 2.8 2.9 2.8 2.9